In recent years, an increase in size of a wafer is demanded, and a wire saw is mainly used to slice a workpiece with this increase in size.
The wire saw is an apparatus that causes a wire (a high-tensile steel wire) to travel at a high speed, presses a workpiece against the wire to cut the workpiece while applying a slurry to the wire and thereby slices the workpiece into many wafers at the same time (see Japanese Patent Laid-open (Kokai) No. H09-262826).
Here, an outline of an example of a conventionally general wire saw is shown in FIG. 3.
As shown in FIG. 3, a wire saw 101 mainly includes a wire 102 for slicing a workpiece, grooved rollers 103 around which the wire 102 is wound, a mechanism 104 for giving the wire 102 a tensile force, a mechanism 105 for feeding the workpiece to be sliced downward, and a mechanism 106 for supplying a slurry at the time of slicing.
The wire 102 is unreeled from one wire reel 107 and reaches the grooved rollers 103 via the tensile-force-giving mechanism 104 composed of a powder clutch (a constant torque motor 109), a dancer roller (a dead weight) (not shown) and the like through a traverser 108. The wire 102 is wound around this grooved rollers 103 for approximately 300 to 400 turns to form a wire row, and then taken up by a wire reel 107′ via the other tensile-force-giving mechanism 104′.
Moreover, each of the grooved rollers 103 is a roller that has a steel cylinder of which a polyurethane resin is pressed in the periphery and that has grooves formed at a fixed pitch on a surface thereof. The wound wire 102 can be driven in a reciprocating direction for a predetermined traveling distance by a driving motor 110.
It is to be noted that the workpiece-feeding mechanism 105 feeds the workpiece, toward the wire 102 wound around the grooved rollers 103 by holding and pushing down the workpiece at the time of slicing the workpiece.
Moreover, nozzles 115 are provided near the grooved rollers 103 and the wound wire 102, and a slurry can be supplied to the wire 102 from a slurry tank 116 at the time of slicing. Additionally, a slurry chiller 117 is connected with the slurry tank 116 so that a temperature of the slurry to be supplied can be adjusted.
With the wire saw 101, an appropriate tensile force is applied to the wire 102 with a wire-tensile-force-giving mechanism 104, and the workpiece is sliced while the wire 102 is caused to travel in a reciprocating direction by the driving motor 110.
The slicing of the workpiece is finished by cutting the workpiece until the wire reaches a pad plate, which holds the workpiece. Then the sliced workpiece is extracted from the wire row by reversing a direction of feeding the workpiece.
As the wire saw for preventing the wire from lifting by being caught on the sliced portion at the time of extracting the workpiece from the wire row, there is disclosed the wire saw having a means for restricting the lift of the wire by pushing against the wire in the vicinity of a wire entrance point of the workpiece with a pair of restricting members, which compose the means for restricting in Japanese Patent Laid-open (Kokai) No. H08-11047.
However, when the present inventors sliced the workpiece into wafers by using the general wire saw as described above and examined a shape of the sliced wafer, a large Warp was generated.
The Warp is one of important qualities for slicing of a semiconductor wafer. Hence, the more quality demand of a product increases, the more demand of reduction of the Warp increases.
As an example of a negative influence on a workpiece quality, there is a problem that a workpiece slicing surface is damaged by the slurry remaining on the workpiece slicing surface at the time of extracting the sliced workpiece from the wire row after slicing the workpiece. There is disclosed the wire saw that enhances a tensile force applied to the wire at the time of extracting the sliced workpiece from the wire row in order to suppress a negative influence on the workpiece slicing surface in Japanese Patent Laid-open (Kokai) No. 2003-275950.